1. Field of the Invention
The present invention generally relates to optical switches and, in particular, to optical switches having servo control mechanisms and focusing components.
2. Background of the Invention
Current optical switches, such as fiber to fiber switches, use various mechanisms to switch light beams from an input to a selected output. For instance, piezoelectric actuators are used to move fibers in the focal plane of lenses to create a directional optical transmitter or receiver. Alternatively, the fiber is held in a fixed position in the center of the focal plane of the lens and the beam is directed to the desired location with one or more moveable mirrors. The output of the beam is determined by controlling the mirrors within the switch. Optical switches can be used to switch light in various applications including fiber to fiber switches and in multi-disk optical disk drives.
In the case of optical disk drives, optical switches can be used to direct a beam of light from a single light source to any one of a number of optical disks. In general, various optical disk drive systems have been proposed for use with multiple optical disks loaded on a rotationally mounted spindle, and such systems have become increasingly popular because of their large storage capabilities. A typical optical disk drive system uses one or more laser sources to transmit a laser beam onto a selected track of an optical disk. In reading applications, the beam reflected from the surface of the optical disk is monitored by a signal detector to reconstruct information stored on the recording surfaces of disks.
Some of the existing multiple disk drive systems use a single head assembly mounted on an elevator carriage, which physically moves within the drive to bring the laser beam to each reflective disk surface. Some of the existing multiple disk drive systems use a multiple head assembly system, where one head assembly is assigned to each of reflective surfaces of the optical disks. Others, such as disclosed in U.S. Pat. No. 5,153,870 to Lee et al., provide a rotary head actuator which employs an optically switchable reflector using removeable index matching fluid to distribute a laser beam from a laser source to one of several optical disks.
These prior art storage devices suffer from various disadvantages. For example, one problem associated with some of the known storage devices is that additional access time is required during positioning of the laser beam between optical disks. This problem is more prevalent when the requested data is dispersed among multiple disk surfaces. Some storage devices are expensive to manufacture and cumbersome to fit into small cases since each head assembly contains a complete set of optical head components, including laser beam source, detector, mirrors and lenses.
The present invention is directed to an optical switch for switching a light beam from at least one optical input to one of a plurality of outputs. The optical switch includes a first moveable mirror for reflecting the light beam from the optical input and a second moveable mirror for reflecting the light beam reflected from the first moveable mirror, wherein the first moveable mirror is adjusted to guide the light beam from the optical input to a selected point on the second moveable mirror, and the second moveable mirror is adjusted to guide the light beam from the first moveable mirror to one of the outputs.
In the optical switch of the present invention, the first and second moveable mirrors are rotatable about at least one pivot axis, and the optical switch further includes a control mechanism to control the rotation of the first and second moveable mirrors about the pivot axis. In one embodiment of the present invention, the first and second moveable mirrors are rotatable about both a first pivot axis and a second pivot axis, and the optical switch further includes a control mechanism to control the rotation of the first and second moveable mirrors about both axes.
In another embodiment, the optical switch includes a plurality of optical inputs, and the first moveable mirror is adjusted to guide the light beam emitted from one of these plurality of optical inputs to a selected point on the second moveable mirror.
In one embodiment of the present invention, the mirror, includes a top reflective surface, a bottom surface opposite the top surface, a magnetic material attached to at least a portion of the bottom surface, and at least one magnetic coil for attracting the magnetic material to rotate the moveable mirrors. In another embodiment, the moveable mirrors also include a support frame, a gimbal frame rotatably connected to the support frame, and a mirror portion rotatably connected to the gimbal frame, wherein the mirror is rotatable about a first axis of rotation and the gimbal frame is rotatable about a second axis of rotation.
In yet another embodiment of the optical switch, the mirror portion further includes a top reflective surface and a bottom surface opposite the top surface, and the optical switch also includes a magnetic material attached to at least a portion of the bottom surface of the mirror portion and at least a portion of the gimbal frame. A first set of magnetic coils for attracting the magnetic material attached to the mirror portion is positioned adjacent to the magnetic material on the mirror portion to rotate the mirror about the first axis of rotation, and a second set of magnetic coils is positioned adjacent to the magnetic material on the gimbal frame for attracting the magnetic material on the gimbal frame to rotate the mirror about the second axis of rotation. A wing structure can be attached non-rotatably to the mirror portion, and the magnetic material attached to the wing structure.
The optical switch of the present invention can also include a damping material disposed between the magnetic material and the magnetic coils. Suitable materials for the dampening material include aluminum and copper. The magnetic coils are electromagnets. The magnetic material can be a permanent magnet that is polarized in a direction perpendicular to the bottom surface or in a direction parallel to the bottom surface.
The present invention is also directed to an adjustable mirror assembly having a support base, a mirror having a reflective surface and connected to the support base by a first flexible pivot, and two linear actuators connected to the mirror by a second flexible pivot and a third flexible pivot, wherein movement of the second and third pivots by the linear actuators provides two degrees of rotational freedom to the reflective surface of the mirror with respect to the first flexible pivot. The linear actuators can be operatively associated with an optical disk drive controller so as to direct an optical beam to a selected disk location. In addition, the linear actuator and the optical disk drive controller can cooperate to manipulate the reflective surface so as to control tracking and focusing of the optical beam with respect to an optical disk.
The present invention is further directed to optical devices such as optical disk drives, which may be enhanced by incorporating one or more of the moveable mirrors of the present invention to effectively switch a laser beam from at least one light source to one of a plurality outputs, such as read/write heads of an optical storage device.
The present invention is also directed to an apparatus and corresponding method for selectively directing a light beam from at least one light source to a number of outputs. The beam-directing apparatus uses at least one moveable mirror having a reflective surface which is capable of changing its orientation to direct the light beam in a selected optical path. In a preferred embodiment, the beam-directing apparatus uses two moveable mirrors, where each moveable mirror is capable of rotating with respect to at least one pivot axis to selectively guide the light beam to one of the outputs.
According to one aspect of the invention, the beam-directing apparatus can be used with an optical disk drive for selectively coupling a beam of light from a laser module to a selected optical disk surface. In a preferred embodiment, the beam-directing apparatus uses two moveable mirrors together with stationary mirrors. Each moveable mirror is capable of rotating with respect to at least one pivot axis to guide the light beam to one of the stationery mirrors. According to the invention, the optical disk drive has a plurality of head members positioned near surfaces of a plurality of optical disks to optically read and/or write information from and onto the optical disks rotatably supported about a spindle. The head members preferably include at least one set of a head mirror and an R/W objective lens located between the head mirror and the respective disk for receiving the beam of light from the beam-directing apparatus and focusing the received light beam onto a selected track of the disk.
According to another aspect of the invention, one or more moveable mirrors, of any suitable type, are used in the optical switching apparatus so as to enable the light beam to be rapidly and accurately guided along a precise optical path, as required by the optical disk drive. The moveable mirrors may include a moveable reflective surface which is adjustable about at least one pivot axis and preferably about two pivot axes. The moveable mirror is associated with a control mechanism for precisely controlling the orientation of the reflective surface in one or both pivot axes. A processor may be coupled to the control mechanisms of the moveable mirrors in order to coordinate their movements to selectively switch the optical path of the laser beam between different optical read/write head members.
According to a further aspect of the invention, a plurality of stationary mirrors is provided, each associated with one of said head members. The stationary mirrors reflective surfaces oriented at a predetermined pivotal angle to deflect the light beam from the second moveable mirror to a respective head member. Although referred to herein as xe2x80x9cstationaryxe2x80x9d, such mirrors may be mounted on and move with an actuator arm, but can be stationary with respect to the mount.
The reading and writing operations are executed by first moving the read/write head associated with such optical disk to a specific target track area thereof. The laser beam emitted by the laser source is reflected by the first and second moveable mirrors to one of the stationary mirrors. A processor controls the movements of the first and second moveable mirrors to precisely guide the light beam to a specific spot on the selected stationary mirror, such that the beam from the stationary mirror is deflected by a head mirror and guided to the center of an R/W objective lens associated with the selected optical disk. The beam reflected from the surface of the optical disk is monitored by a signal detector to reconstruct information stored on the recording surface of the disk.
In one aspect of the invention, the optical switching apparatus includes a feedback mechanism for monitoring the position of the moveable mirrors. The feedback mechanism may include an auxiliary light source for generating an auxiliary light beam and a position sensitive detector for detecting the auxiliary light beam deflected from the moveable mirror in order to accurately determine the position thereof.
In another aspect of the invention, an optical disk drive is provided in which a control mechanism is used with a beam-directing apparatus for controlling the operations of the beam-directing apparatus. The beam-directing apparatus may include two moveable mirrors, the orientations of which are precisely controlled by control mechanism. The moveable mirrors together with the control mechanism are capable of rapidly and accurately guiding a light beam from a selected light source to a precise optical path.
In yet another aspect of the invention, an optical disk drive is provided in which the size of the beam reflected onto an optical disk surface may be controllable by a beam apparatus. The focusing of the beam on an optical disk surface may be controlled with use of two moveable mirrors, accomplished by controlling the position of the laser beam impinging upon the second moveable mirror with the first moveable mirror. In a related aspect of the invention, the tracking of the beam on the optical disk surface may also be controlled by controlling the position of the laser beam impinging upon the second moveable mirror with the first moveable mirror.
In a further aspect of the invention, a moveable mirror is provided. The moveable mirror includes a reflector rotatable about at least one pivot axis. The reflector is adjustably supported between a support surface and at least one actuator so as to cause the reflector to rotate about pivot axis in either direction as the actuator moves toward or away the reflector. This moveable mirror may be used in the read/write head members so that the orientation of its reflector may be adjusted, as required for focusing and tracking needs.
The present invention is also directed to servo mechanisms to control the alignment of the moveable mirrors in the optical switch and to control the alignment of the optical inputs and outputs. Various servo mechanisms are possible as shown, for example, in U.S. Provisional Application No. 60/088,240, the entire disclosure of which is incorporated herein by reference. Focusing components such as focusing lens are also used in the optical switch of the present invention to maximize optical focusing.